Measurements of DNA polymerase protein levels and polymerase activity through the naturally synchronous mitotic cycle of Physarum polycephalum show that active DNA polymerase-alpha is synthesized throughout the G2 phase, in step with the profile of general protein biosynthesis. Three main components of P. poly-cephalum DNA polymerase of 200, 112 and 70 kDa were found to be immunologically related.